springboot注解方式，@Autowire和有参构造和无参构造使用哪个创建对象

springboot注解方式，@Autowire和有参构造和无参构造使用哪个创建对象

构造测试条件

① application.yml

ruoyi.name = ruoyi
ruoyi.age = 12
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② pojo.Person类

@Data
@Component 
@NoArgsConstructor
@AllArgsConstructor
public class Person {
    @Value("${ruoyi.name}")
    private String name;
    @Value("${ruoyi.age}")
    private Integer age;
}

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③ 启动类

@SpringBootApplication
@Slf4j
public class Application {

    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(Application.class, args);

            log.info("{}",run);

    }

}
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第一种 controller

@RestController
public class HelloController {

    @Autowired
    private Person person;

    public HelloController(Person person) {

        this.person = new Person("2",2);
    }

    public HelloController() {
        person = new Person("1",1);
    }
}
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测试：

第二种 controller

@RestController
public class HelloController {

    // @Autowired
    private Person person;

    public HelloController(Person person) {

        this.person = new Person("2",2);
    }

    public HelloController() {
        person = new Person("1",1);
    }
}
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测试：

第三种 controller

@RestController
public class HelloController {

    // @Autowired
    private Person person;

    public HelloController(Person person) {

        this.person = new Person("2",2);
    }

//    public HelloController() {
//        person = new Person("1",1);
//    }
}

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测试：

报错了，Spring容器会报错，需要修改@Autowired(required = false)即可，如下修改：

@RestController
public class HelloController {

    @Autowired
    private Person person;

    @Autowired(required = false)
    public HelloController(Person person) {

        this.person = new Person("2",2);
    }

    @Autowired(required = false)
    public HelloController() {
        person = new Person("1",1);
    }
}

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测试：

第五种 controller

@RestController
public class HelloController {

//    @Autowired
    private Person person;

    @Autowired(required = false)
    public HelloController(Person person) {
        this.person = new Person("2",2);
    }

    @Autowired(required = false)
    public HelloController() {
        person = new Person("1",1);
    }
}
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测试：

这样的话，Spring会根据参数个数进行排序，参数个数越多，优先级越高，这样上面的代码就会调用第一个构造函数

第六种 controller

@RestController
public class HelloController {

//    @Autowired
    private Person person;

    @Autowired(required = false)
    public HelloController(Person person) {

        this.person = new Person("2",2);
    }

    // @Autowired(required = false)
    public HelloController() {
        person = new Person("1",1);
    }
}
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测试：

总结：

1、Spring在实例化对象的时候一旦找到一个它认为合适的构造方法，就会直接实例化对象，不会继续寻找其他构造方法。

2、@Autowire写在属性上永远第一，

3、要是没有@Autowire写在属性上，取写在构造方法上的，要是有多个急需要加@Autowired(required = false)，参数多的为主

4、要是都没有，就使用无参构造创建对象

5、只有有参构造，就使用有参构造创建对象